Welcome to WebmasterWorld Guest from 18.104.22.168
They have some 20 or 30 domains pointing to their main, I'm not sure but doesn't look like parking, in fact if you type any of these you are redirected to main (probably by 301 or meta tag, redirect).
To me is clearly an attempt to monopolize the area and looks very spammy.
So what does Google think about it?
Is that a Google-hated practice considered spam or it's ok?
Should I go and register one hundred domains like them and point everyting to my real site ore I just wait they be penalized and stop spamming?
But if you are worried, don't be. I know of businesses that 301 redirect over a thousand domain names to one principal site. As long as you don't continue to market and get backlinks for the old domains, they see nothing unfortunate happening at Google.
The main site has links at the bottom of every page that point to more than a dozen different domain names.
Each of those other domain names simply serves a 301 redirect back to the place that you just came from.
If that isn't junk, then I don't know what is. I have no real idea what it is attempting to achieve. I guess it is trying to pass extra PageRank back to itself.